In the past, the semiconductor industry used various methods and structures to form voltage reference circuits. The voltage reference circuits generally were used to supply a stable reference voltage for use by other circuits such as a comparator circuit. One commonly used design technique to form the voltage reference circuits used a bandgap reference as a portion of the voltage reference circuit. One design parameter for the prior voltage reference circuits was to reduce variations in the reference voltage that resulted from variations in temperature. One example of a prior voltage reference circuit that included temperature compensation was disclosed in U.S. Pat. No. 7,692,476, titled “Temperature Compensating Circuit” issued to Ryoichi Anzai on Apr. 6, 2010. However, such prior voltage reference circuits did not provide sufficient temperature stabilization over an extended temperature range.
Accordingly, it would be advantageous to have a voltage reference circuit that has improved temperature compensation. It would be of further advantage for the structure and method to be cost efficient to implement.
For simplicity and clarity of illustration, elements in the figures are not necessarily to scale, and the same reference characters in different figures denote the same elements. Additionally, descriptions and details of well-known steps and elements are omitted for simplicity of the description. As used herein current carrying electrode means an element of a device that carries current through the device such as a source or a drain of an MOS transistor or an emitter or a collector of a bipolar transistor or a cathode or anode of a diode, and a control electrode means an element of the device that controls current flow through the device such as a gate of an MOS transistor or a base of a bipolar transistor. Although the devices are explained herein as certain n-channel or p-channel devices, or certain n-type or p-type doped regions, a person of ordinary skill in the art will appreciate that complementary devices are also possible in accordance with embodiments of the present invention. It will be appreciated by those skilled in the art that the words during, while, and when as used herein are not exact terms that mean an action takes place instantly upon an initiating action but that there may be some small but reasonable delay, such as a propagation delay, between the reaction that is initiated by the initial action. The use of the words approximately, about, or substantially means that a value of an element has a parameter that is expected to be very close to a stated value or position. However, as is well known in the art there are always minor variances that prevent the values or positions from being exactly as stated. It is well established in the art that variances of up to about ten percent (10%) (and up to twenty percent (20%) for semiconductor doping concentrations) are regarded as reasonable variances from the ideal goal of exactly as described.